Sift together flour, baking powder, baking soda and
salt and set aside. In a bowl beat butter until fluffy. Add vanilla and 1 egg
at a time, mixing well between additions. Add dry ingredients and mix well. Refrigerate
for about 1 hour. Form 2 logs with about 5cm in
diameter, wrap in waxed paper and refrigerate for about 8 hours.

Cut into 3mm thick
discs and place them on a tray lined with waxed paper. Leave about 3cm space
around each disc to allow them to spread out.

Place in pre-heated oven at
180ºC for 10 minutes. Remove and let cool on a rack. The dough will last in the
refrigerator for about a week, so you can always have freshly baked cookies.
You can also freeze the dough and slice into discs without having to thaw previously.